The present invention relates to a manufacturing tool for a fluid bearing device in which constituent parts can be exchanged for new ones so that the life of a tool is improved greatly, and particularly to a manufacturing tool for forming a dynamic pressure generating groove on a fluid bearing device.
A manufacturing tool a groove-including fluid bearing device shown in FIG. 10 is known as a related manufacturing tool for forming a dynamic pressure generating groove in a fluid bearing device. The manufacturing tool a bearing device is provided for forming a dynamic pressure generating groove in an inner circumferential surface of a fluid bearing device. The apparatus comprises a shaft 21, rolling balls 23, and a ball gauge 24. A circumferential groove 22 is provided in the outer circumference of the shaft 21. A plurality of holes are formed in the cylindrical ball gauge 24. The rolling balls 23 dropped into the holes respectively are fitted into the circumferential groove 22 so that the shaft 21 and the ball gauge 24 are connected to each other. The rolling balls 23 are partially protruded from the outer circumferential surface of the ball gauge 24. When the shaft 21 is axially moved while being rotated in the condition that the manufacturing tool is inserted in the inner circumference of a sleeve 25 as a work piece, the rolling balls 23 come into pressure contact with an inner circumference of the sleeve 25 to thereby form predetermined dynamic pressure generating grooves in the inner circumference of the sleeve
In the related art shown in FIG. 10, however, the rolling balls 23 always touch fixed positions of the groove 22. Hence, when grooving is performed, abrasion of the rolling balls 23 against the groove 22, especially against the bottom surface of the groove 22, is so rapid that the tool must be exchanged for new one frequently. Moreover, the center of the tool must be aligned with the center of a product accurately whenever the tool is exchanged for new one. There was a problem that a great deal of time was required for this arrangement.
Moreover, the circumferential edges of the holes formed in the ball gauge 24 and receiving the rolling balls 23 dropped down thereinto are caulked or a stop ring is attached so that the rolling balls 23 are prevented from drifting or dropping out. Hence, even in the case where a part of the rolling balls 23 has worn out, it is impossible to exchange only the part. The whole tool must be exchanged. There was also a problem that the cost of the tool became high. Moreover, the rolling balls 23 cannot be fixed sufficiently by the method using caulking or the stop ring for preventing the rolling balls 23 from dropping out. Hence, the rolling balls 23 may drop out when grooving is performed. There was a further problem that the number of grooves ran short. Moreover, when grooving is performed, the rolling balls 23 cannot always smoothly rotate. There was a further problem that the grooves after grooving became different in depth.
The present invention is provided to solve the aforementioned problems in the related art and an object of the present invention is to provide a manufacturing tool for a fluid bearing device, in which parts of a tool for producing the fluid bearing device can be individually exchanged for new ones so that, when a part has worn out, only the part can be exchanged for a new one to thereby elongate the life of the tool as a whole and reduce the cost of the tool as whole.
In order to achieve the above object, according to the present invention, there is provided a manufacturing tool inserted in a hole formed in a work piece for forming a fluid bearing groove on an inner peripheral surface of the hole, comprising:
a tool shaft being rotated in the hole while being moved in an axial direction thereof;
a plurality of balls rotatably supported on an outer peripheral face of the tool shaft, which are to be abutted against the inner peripheral surface of the hole to form the fluid bearing groove thereon in accordance with the movement of the tool shaft;
a retainer detachably fitted on the outer peripheral face of the tool shaft so as to retain the balls on the tool shaft;
a fixing member detachably fitted with the tool shaft so as to fix the retainer on the tool shaft,
wherein the balls can be replaced when the fixing member and the retainer is detached from the tool shaft.
According to the above configuration, abraded parts such as balls can be partially exchanged for new ones. It is unnecessary to exchange the manufacturing tool entirely. The cost of the manufacturing tool can be reduced greatly.
Preferably, the manufacturing tool further comprises a ball bearing member accommodated in an axial hole formed in the tool shaft so as to be axially movable therein while bearing the balls in bearing recesses formed on an outer peripheral face thereof. Here, the bearing recesses are shaped such that the balls are situated at different positions therein in accordance with the direction of the axial movement of the tool shaft.
According to the above configuration, when grooving is performed, a load of the balls applied on the ball bearing member can be distributed into a forward stroke and a backward stroke. Hence, the quantity of abrasion of the balls, the ball bearing member, etc. can be reduced, so that the life of the manufacturing tool can be elongated.
Preferably, the ball bearing member is a shaft member having a circular cross section. Here, the largest diameter of the ball bearing member is made smaller than the diameter of the hole of the work piece so as to define a clearance therebetween. The ball bearing member can be made eccentric and inclined with respect to the axial center of the tool shaft in a range of the clearance.
According to the above configuration, accuracy can be kept high on the basis of the floating effect even in the case where the center of the tool shaft is aligned with the center of the work piece incorrectly. Hence, shortening the time required for arrangement of the alignment and great improvement of quality can be achieved.
According to the present invention, there is also provided a manufacturing tool for forming a fluid bearing groove on an outer peripheral surface of a work piece, comprising:
a tool shaft formed with an axial hole extending in an axial direction thereof, which is to be rotated while being moved in the axial direction around the work piece inserted in the axial hole;
a plurality of balls rotatably supported on an inner peripheral face of the tool shaft, which are to be abutted against the outer peripheral surface of the work piece to form the fluid bearing groove in accordance with the movement of the tool shaft;
a retainer detachably fitted on the inner peripheral face of the tool shaft so as to retain the balls on the tool shaft;
a fixing member detachably fitted with the inner peripheral face of the tool shaft so as to fix the retainer on the tool shaft,
wherein the balls can be replaced when the fixing member and the retainer is detached from the tool shaft.
According to the above configuration, abraded parts such as balls can be partially exchanged for new ones. It is unnecessary to exchange the manufacturing tool as a whole. The cost of the manufacturing tool can be reduced greatly.
Preferably, the manufacturing tool further comprises a ball bearing member provided on an outer periphery of the tool shaft so as to be movable in the axial direction of the tool shaft while bearing the balls in bearing recesses formed on an inner peripheral face thereof. Here, the bearing recesses are shaped such that the balls are situated at different positions therein in accordance with the direction of the axial movement of the tool shaft.
According to the above configuration, when grooving is performed, a load of the balls applied on the ball bearing member can be distributed into a forward stroke and a backward stroke. Hence, the quantity of abrasion of the balls, the ball bearing member, etc. can be reduced, so that the life of the manufacturing tool can be elongated.
Preferably, the ball bearing member is provided as a cylindrical member in which an inner periphery thereof has a circular cross section. Here, a clearance is formed between the inner periphery of the ball bearing member and the outer periphery of the tool shaft.
According to the above configuration, accuracy can be kept sufficiently on the basis of the floating effect even in the case where the center of the tool shaft is aligned with the center of the work piece incorrectly. Hence, shortening the time required for arrangement of the alignment and great improvement of quality can be achieved.